Charge carrier transport facilitated by strain

ABSTRACT

A semiconductor structure and formation thereof. The semiconductor structure has a first semiconductor layer with a first lattice structure and a second epitaxial semiconductor layer that is lattice-matched with the first semiconductor layer. At least two source/drain regions, which have a second lattice structure, penetrate the second semiconductor layer and contact the first semiconductor layer. A portion of the second semiconductor layer is between the source/drain regions and has a degree of uniaxial strain that is based, at least in part, on a difference between the first lattice structure and the second lattice structure.

BACKGROUND OF THE INVENTION

The present invention relates generally to the field of semiconductorstructures, and more particularly to the inducement of strain onfield-effect transistor channels.

A pure semiconductor is a poor electrical conductor as a consequence ofhaving just the right number of electrons to completely fill its valencebonds. Through various techniques (e.g. doping or gating), thesemiconductor can be modified to have an excess of electrons (becomingan n-type semiconductor) or a deficiency of electrons (becoming a p-typesemiconductor). In both cases, the semiconductor becomes much moreconductive (the conductivity can be increased by one million-fold ormore). Semiconductor devices exploit this effect to shape electricalcurrent. The study of semiconductor materials is an important area ofmaterial science research due to their application in devices such astransistors and therefore computers.

The most commonly used semiconductor materials are crystalline inorganicmaterials, which are classified according to the periodic table groupsof their constituent atoms and also whether they are composed of asingle element or more than one element. For example, silicon (Si) is acommon semiconductor material and it is a group IVA element so it isclassified as a group IV elemental semiconductor. Silicon-germanium(SiGe) is an alloy of two different group IVA elements so it isclassified as a group IV compound semiconductor. When a semiconductor iscomposed of two or more elements from different periodic table groups,indicating compound vs. element is no longer necessary. Thus, leadsulfide (PbS) is composed of a group IVA element (Pb) and a group VIAelement (S) so it is referred to as a IV-VI semiconductor. Likewise,indium phosphide (InP) is composed of a group IIIA element (In) and agroup VA element (P) so it is a III-V semiconductor. There are severalother classes of semiconductors of varying popularity (e.g., II-VI,I-VII, V-VI, II-V). Finally, semiconductors composed of two differentelements are binary (e.g., InP), semiconductors with three differentelements are ternary (e.g. the III-V semiconductor indium galliumarsenide (InGaAs)), and those with four and five different elements arequaternary and quinary, respectively.

Doping is the introduction of impurities to a semiconductor in order tovary its electronic nature. Depending on how it is doped, asemiconductor can be made to be n-type or p-type. For example, Si can bemade n-type by doping with phosphorus. Phosphorus (P) has one morevalence electron than Si and its incorporation into the Si crystallattice creates a preponderance of nonbonding electrons, which areavailable as negative charge carriers. The “n” in n-type stands for“negative” and indicates that electrons are the majority chargecarriers. If Boron were used as the dopant instead of P, the Si wouldbecome a p-type semiconductor. Boron (B) has one less valence electronthan Si, which means it can only form covalent bonds with three Si atomsin the Si crystal lattice. The absence of an electron where one couldexist in an atomic lattice is referred to as a hole. Electrons canmigrate hole-to-hole leaving a hole behind each time. Thus, p-typesemiconductors have moving holes as majority charge carriers and the “p”stands for “positive.”

Field-effect transistors (FETs) are transistors that employ an electricfield to control the conductivity of a channel in which one of the twotypes of charge carriers may travel. A FET is composed of a source and adrain connected by the channel through which the charge carriers,electrons or holes, pass when voltage is applied to a gate. The gatesits over the channel separated by an insulating material referred to asthe gate dielectric. Applying voltage to the gate changes the amount ofcharge carriers in the channel thereby controlling the current in thedevice.

Charge carrier transport that is typically described by mobility throughFET channels is an important factor for optimal performance. One waycharge carrier transport can be modulated is through strain. Forexample, strained channels have been successfully integrated into Si-and Ge-based metal oxide semiconductor FETs (MOSFETs) to enhance carriermobility. Strain can be in the form of biaxial or uniaxial strain andmay be compressive or tensile. A biaxial strained crystal has stressintroduced in two directions (x-y) along its surface whereas a uniaxialstrained crystal has stress introduced in only one direction.Compressive strain occurs when the crystal lattice is being compressedwhereas tensile strain occurs when the crystal lattice is beingstretched. In silicon, compressive strain facilitates hole mobility andtensile strain facilitates electron mobility.

Enhancing charge carrier transport for FETs through the use of uniaxialstrain is an ongoing challenge. For example, high mobility, narrow bandgap III-V materials are considered strong contenders to replacestrained-Si channels. However, even though these III-V materialsdemonstrate high electron mobility, they are less promising for holetransport due to intrinsic lower hole mobility when compared withstrained-Si. Eventual integration of III-V based semiconductors asMOSFET channels requires both high performance n- and p-MOSFETS. Thus,methods for fabricating III-V-based p-FETs with uniaxial compressivestrained channel regions in order to improve hole transport is ofsignificant interest.

SUMMARY

According to one embodiment of the present disclosure, a structurecomprising a semiconductor structure. The semiconductor structureincludes a first semiconductor layer with a first lattice structure anda second epitaxial semiconductor layer that is lattice-matched with thefirst semiconductor layer. At least two source/drain regions, which havea second lattice structure, penetrate the second semiconductor layer andcontact the first semiconductor layer. A portion of the secondsemiconductor layer is between the source/drain regions and has a degreeof uniaxial strain that is based, at least in part, on a differencebetween the first lattice structure and the second lattice structure.

According to one embodiment of the present disclosure, a method offorming a semiconductor structure is provided. The method includingforming a layer of a first semiconductor material on top of a layer of asemi-insulating semiconductor material. The first semiconductor materialand the semi-insulating semiconductor material are lattice-matched. Thelayer of first semiconductor material is etched to a depth that, atleast, exposes the semi-insulating semiconductor material and forms asemiconductor channel region with a first end and a second end. A firstsource/drain region is formed at the first end of the semiconductorchannel region and a second source/drain region is formed at the secondend of the semiconductor channel region. The first source/drain regionand the second source/drain region include a second semiconductormaterial. The second semiconductor material is lattice-mismatched to thefirst semiconductor material and to the semi-insulating semiconductormaterial.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The following detailed description, given by way of example and notintended to limit the disclosure solely thereto, will best beappreciated in conjunction with the accompanying drawings, in which:

FIG. 1A illustrates a cross-sectional view depicting a semi-insulated(SI) semiconductor layer, in accordance with an exemplary embodiment ofthe present invention.

FIG. 1B illustrates a cross-sectional view depicting the formation of asemiconductor layer on the SI semiconductor layer of FIG. 1A, inaccordance with an exemplary embodiment of the present invention.

FIG. 2A illustrates a cross-sectional view depicting the formation of aplurality of gate structures on the semiconductor layer of FIG. 1B, inaccordance with an exemplary embodiment of the present invention.

FIG. 2B illustrates a cross-sectional view depicting the removal of thesemiconductor layer along with a portion of the SI semiconductor layeradjacent to the gate structures from the structure depicted in FIG. 2A,thereby defining semiconductor channel regions and providing an etchedSI semiconductor layer in accordance with an exemplary embodiment of thepresent invention.

FIG. 3A illustrates a cross-sectional view depicting the formation ofsource/drain regions on the lower surfaces of the etched SIsemiconductor layer and adjacent to the semiconductor channel regions ofthe structure depicted in FIG. 2B, in accordance with an exemplaryembodiment of the present invention.

FIG. 3B illustrates a cross-sectional view depicting recessedsource/drain regions in a structure analogous to the one depicted inFIG. 3A, in accordance with an exemplary embodiment of the presentinvention.

FIG. 4A illustrates a cross-sectional view depicting the formation of aplurality of sacrificial gates with adjoining spacers on thesemiconductor layer of FIG. 1B, in accordance with an exemplaryembodiment of the present invention.

FIG. 4B illustrates a cross-sectional view depicting the removal of thesemiconductor layer along with a portion of the SI semiconductor layeradjacent to the spacers from the structure depicted in FIG. 4A, therebyforming semiconductor channel regions and an etched SI semiconductorlayer in accordance with an exemplary embodiment of the presentinvention.

FIG. 5A illustrates a cross-sectional view depicting the formation ofsource/drain regions on the lower surfaces of the etched SIsemiconductor layer and adjacent to the semiconductor channel regionsand spacers of the structure depicted in FIG. 4B, in accordance with anexemplary embodiment of the present invention.

FIG. 5B illustrates a cross-sectional view depicting the removal of hardmask regions from the structure of FIG. 5A, formation of gate dielectriclayers along the exposed spacer sidewalls and exposed semiconductorchannel region surfaces, and formation of gate conductors, in accordancewith an exemplary embodiment of the present invention.

FIG. 6A illustrates a cross-sectional view depicting semiconductorchannel regions on top of the upper surfaces of an etched SIsemiconductor layer with hard mask regions on top of said semiconductorchannel regions, in accordance with an exemplary embodiment of thepresent invention.

FIG. 6B illustrates a cross-sectional view depicting the formation ofsource/drain regions on the lower surfaces of the etched SIsemiconductor layer and adjacent to the semiconductor channel regionsand hard mask regions of the structure depicted in FIG. 6A, inaccordance with an exemplary embodiment of the present invention.

FIG. 7A illustrates a cross-sectional view depicting the removal of hardmask regions from the structure depicted in FIG. 6B, in accordance withan exemplary embodiment of the present invention.

FIG. 7B illustrates a cross-sectional view depicting the formation ofspacers adjacent to the exposed sides of the source/drain regions of thestructure depicted in FIG. 7A, in accordance with an exemplaryembodiment of the present invention.

FIG. 8A illustrates a cross-sectional view depicting the formation ofgate dielectric layers over the exposed surfaces of the semiconductorchannel regions and spacers of the structure depicted in FIG. 7B, inaccordance with an exemplary embodiment of the present invention.

FIG. 8B illustrates a cross-sectional view depicting the formation ofgate conductors on the gate dielectric layers of the structure depictedin FIG. 8A, in accordance with an exemplary embodiment of the presentinvention.

FIG. 8C illustrates a cross-sectional view depicting recessedsource/drain regions in a structure analogous to the one depicted inFIG. 8B, in accordance with an exemplary embodiment of the presentinvention.

The drawings are not necessarily to scale. The drawings are merelyschematic representations, not intended to portray specific parametersof the invention. The drawings are intended to depict only typicalembodiments of the invention. In the drawings, like numbering representslike elements.

DETAILED DESCRIPTION

Exemplary embodiments now will be described more fully herein withreference to the accompanying drawings, in which exemplary embodimentsare shown. In the following detailed description, numerous specificdetails are set forth in order to provide a thorough understanding ofvarious embodiments of the invention. However, it is to be understoodthat embodiments of the invention may be practiced without thesespecific details. As such, this disclosure may be embodied in manydifferent forms and should not be construed as limited to the exemplaryembodiments set forth herein. Rather, these exemplary embodiments areprovided so that this disclosure will be thorough and complete and willfully convey the scope of this disclosure to those skilled in the art.In the description, details of well-known features and techniques may beomitted to avoid unnecessarily obscuring the presented embodiments.

As described below in conjunction with FIGS. 1-8, embodiments mayinclude methods of forming field-effect transistors (FETs) that haveuniaxial strained channel regions separating the source device from thedrain device. The methods described below in conjunction with FIGS. 1-8may be incorporated into typical semiconductor fabrication processes.

For purposes of the description hereinafter, terms such as “upper”,“lower”, “right”, “left”, “vertical”, “horizontal”, “top”, “bottom”, andderivatives thereof shall relate to the disclosed structures andmethods, as oriented in the drawing figures. Terms such as “above”,“overlying”, “atop”, “on top”, “positioned on” or “positioned atop” meanthat a first element, such as a first structure, is present on a secondelement, such as a second structure, wherein intervening elements, suchas an interface structure may be present between the first element andthe second element. The term “direct contact” means that a firstelement, such as a first structure, and a second element, such as asecond structure, are connected without any intermediary conducting,insulating or semiconductor layers at the interface of the two elements.

In the interest of not obscuring the presentation of embodiments of thepresent invention, in the following detailed description, someprocessing steps or operations that are known in the art may have beencombined together for presentation and for illustration purposes and insome instances may have not been described in detail. In otherinstances, some processing steps or operations that are known in the artmay not be described at all. It should be understood that the followingdescription is rather focused on the distinctive features or elements ofvarious embodiments of the present invention.

As used herein, terms such as “depositing”, “forming”, and the likerefer to the disposition of layers or portions of materials in thepresent embodiments. Such processes may not be different than in thestandard practice of the art of FET fabrication. Such practice includebut are not limited to, metalorganic chemical vapor deposition (MOCVD),atomic layer deposition (ALD), chemical vapor deposition (CVD),low-pressure chemical vapor deposition (LPCVD), plasma enhanced chemicalvapor deposition (PECVD), ultrahigh vacuum chemical vapor deposition(UHVCVD), physical vapor deposition, sputtering, plating, evaporation,ion beam deposition, electron beam deposition, laser assisteddeposition, chemical solution deposition, or any combination of thosemethods.

As used herein, the term “lattice-matched” and the like refer toadjoining epitaxial semiconductor materials (including SI semiconductormaterials), which have essentially the same lattice constants and,hence, strain is not induced by the epitaxial growth of a layer that islattice-matched to the substrate upon which it is deposited Likewise,the term “lattice-mismatched” and the like refer to adjoining epitaxialsemiconductor materials (including SI semiconductor materials), which donot have essentially the same lattice constants and, hence, strain isinduced by the epitaxial growth of one of the materials next to or ontop of the lattice-mismatched material.

As used herein, semiconductor structures refer to one or more physicalstructures that comprise semiconductor devices.

The present invention will now be described in detail with reference tothe Figures.

FIG. 1A illustrates a cross-sectional view depicting a SI semiconductorlayer 110, in accordance with an exemplary embodiment of the presentinvention. In various embodiments, SI semiconductor layer 110 is anepitaxial layer of an SI semiconductor lattice-matched to a gradedbuffer layer, which is in turn deposited onto a silicon substrate. In anexemplary embodiment, SI semiconductor layer 110 is deposited on top ofa virtual III-V on Silicon (Si) substrate. For example, SI semiconductorlayer 110 is a layer of epitaxial SI indium phosphide (InP). InP isturned into an SI semiconductor by doping it with impurities such asiron (Fe) or chromium (Cr), which act as traps for free carriers. Thethickness of a typical SI InP layer ranges from about 100 nm to about5000 nm.

FIG. 1B illustrates a cross-sectional view depicting the formation of asemiconductor layer 115 on the SI semiconductor layer 110 of FIG. 1A, inaccordance with an exemplary embodiment of the present invention. Invarious embodiments, semiconductor layer 115 is lattice-matched to theSI semiconductor crystal of SI semiconductor layer 110. In oneembodiment, the semiconductor layer 115 is a III-V semiconductormaterial that is lattice-matched to SI semiconductor layer 110. Forexample, SI semiconductor layer 110 is composed of epitaxial Fe-dopedInP and semiconductor layer 115 is a semiconductor material that islattice-matched to Fe-doped InP, such as In_(0.53)Ga_(0.47)As.

FIG. 2A illustrates a cross-sectional view depicting the formation of aplurality of gate structures on the semiconductor layer 115 of FIG. 1B,in accordance with an exemplary embodiment of the present invention. Thegate structures include gate conductors 220-222, spacers 205-210, andgate dielectrics 230-232. Gate conductors 220, 221, and 222 restdirectly on top of gate dielectrics 230, 231, and 232, respectively andare in contact between spacer pairs 205/206, 207/208, 209/210,respectively. Gate conductors 220-222 are composed of conductivematerial, typically metals. Spacers are composed of an insulator such assilicon dioxide (SiO₂) or silicon nitride (Si₃N₄). Gate dielectrics230-232 are also composed of an insulator, typically SiO₂ or a high-κdielectric metal oxide such as hafnium oxide, hafnium silicon oxide,hafnium silicon oxynitride, lanthanum oxide, lanthanum aluminum oxide,zirconium oxide, zirconium silicon oxide, zirconium silicon oxynitride,tantalum oxide, titanium oxide, barium strontium titanium oxide, bariumtitanium oxide, strontium titanium oxide, yttrium oxide, aluminum oxide,lead scandium tantalum oxide, and lead zinc niobate. The formation ofgate structures as embodied by FIG. 2A is well understood by thoseskilled in the art and, as such, a detailed description of suchprocesses is not presented herein.

FIG. 2B illustrates a cross-sectional view depicting the removal of thesemiconductor layer 115 along with a portion of the SI semiconductorlayer 110 adjacent to the gate structures from the structure depicted inFIG. 2A, thereby defining the device's semiconductor channel regions240-242 and providing etched SI semiconductor layer 245 in accordancewith an exemplary embodiment of the present invention. In thisembodiment, reactive ion etching (RIE) removes all of the semiconductormaterial and a portion of the SI semiconductor material between the gatestructures to create trenches 250 and 255. The gate structures serve asa mask, so the etched trenches 250 and 255 are said to be self-alignedto the channel regions 240-242. Although the embodiment described iscreated using RIE, other dry etching processes will work to obtain theshown anisotropic etch. In this embodiment, semiconductor channelregions 240, 241, and 242 rest on top of the highest surfaces of etchedSI semiconductor layer 245 and underneath the three gate structures. Thesemiconductor channel regions 240-242 and the upper sidewalls oftrenches 250 and 255 are composed of the semiconductor material ofsemiconductor layer 115 (FIG. 2A). The etched SI semiconductor layer 245as well as the lower sidewalls and floors of trenches 250 and 255 arecomposed of the SI semiconductor material of SI semiconductor layer 110.

FIG. 3A illustrates a cross-sectional view depicting the formation ofsource/drain regions 360 and 365 on the lower surfaces of the etched SIsemiconductor layer 245 and adjacent to the semiconductor channelregions 240-242 of the structure depicted in FIG. 2B, in accordance withan exemplary embodiment of the present invention. In variousembodiments, source/drain regions 360 and 365 are composed ofsemiconductor material that is lattice-mismatched to the semiconductormaterial of semiconductor channel regions 240-242 as well aslattice-mismatched to the SI semiconductor material of etched SIsemiconductor layer 245. In an exemplary embodiment, semiconductorchannel regions 240-242 are composed of a III-V semiconductor material,etched SI semiconductor layer 245 includes a top layer of epitaxial SIsemiconductor material that is a lattice-matched to the III-Vsemiconductor material, and source/drain regions 360 and 365 arecomposed of a III-V semiconductor material that is lattice-mismatchedwith both semiconductor channel regions 240-242 and the top layermaterial of etched SI semiconductor layer 245. In one example, SIsemiconductor layer 245 is composed of epitaxial Fe-doped InP,semiconductor channel regions 240-242 are composed of a semiconductormaterial that is lattice-matched to Fe-doped InP, such asIn_(0.53)Ga_(0.47)As, and source/drain regions 360 and 365 are composedof In_(y)Ga_((1−y))As where y>0.53. In this exemplary embodiment,semiconductor channel regions 240-242 experience compressive uniaxialstrain because the source/drain regions 360 and 365 have a largerlattice constant than the semiconductor channel regions 240-242.Compressive uniaxial strain enhances charge carrier transport in p-FETdevices. In another exemplary embodiment, the composition of channels240-242 remains In_(0.53)Ga_(0.47)As, etched SI semiconductor layer 245remains epitaxial Fe-doped InP, but source/drain regions 360 and 365 arecomposed of In_(y)Ga_((1−y))As where y<0.53. In this exemplaryembodiment, semiconductor channel regions 240-242 exhibit tensileuniaxial strain because the source/drain regions 360 and 365 have asmaller lattice constant than the semiconductor channel regions 240-242.Tensile uniaxial strain enhances charge carrier transport in n-FETdevices.

Using the above example, the deposition of source/drain regions 360 and365 can be done using a metal-organic chemical vapor deposition (MOCVD)reactor with trimethylindium (TMIn) as the indium source,trimethylgallium (TEG) as the gallium source, and arsine (AsH₃) as thearsenic source. In such embodiment of the invention, the depositiontemperatures may typically range from 400° C. to 650° C. The source anddrain regions 360 and 365 also need to be doped. Doping of asemiconductor is typically achieved by using impurities that substitutea group III or a group V atom. For example, when In_(0.53)Ga_(0.47)As isused, impurities such as silicon (Si), tin (Sn), selenium (Se), andtellurium (Te) would make the semiconductor to be n-type where majoritycarriers would be electrons. When carbon (C), beryllium (Be), or zinc(Zn) are used the In_(0.53)Ga_(0.47)As semiconductor would be p-typedoped and majority carriers would comprise holes. For n-FET devicesn-type doping is used in the source and drain region, while for p-FETsdevices p-type doping is used. In-situ silicon doping may be practicedduring the deposition of the In_(0.53)Ga_(0.47)As semiconductor. Forexample, when MOCVD growth is used silane (SiH₄) may be added to the gasmixture during the deposition of source and drain to obtain Si doping.Other precursors that may be used are silicon tetrabromide (SiBr₄) andsilicon tetrachloride (SiCl₄). To obtain p-type doping, carbontetrabromide (CBr₄) may be used as the carbon source.

FIG. 3B illustrates a cross-sectional view depicting recessedsource/drain regions 370 and 375 in a structure analogous to the onedepicted in FIG. 3A, in accordance with an exemplary embodiment of thepresent invention. The elements seen in the embodiment exemplified byFIG. 3B are analogous to those in FIG. 3A. Gate conductors 320-322 havespacers 305-310 adjacent to them and in direct contact. Gate dielectrics330-332 separate the conducting gate conductors from the semiconductorchannel regions 340-342. Source/drain regions 370 and 375 rest on thelower surfaces of etched SI semiconductor layer 345 and are adjacent toat least one semiconductor channel region. This exemplary embodiment hasat least 2 fundamental differences compared to the FIG. 3A embodiment:i) The etches in etched SI semiconductor layer 345 include a lateraletch, which is typically practiced with a wet etching process; and ii)bottom portions of source/drain region 370 are wedged underneathsemiconductor channel regions 340 and 341 and bottom portions ofsource/drain region 375 are wedged underneath semiconductor channelregions 341 and 342. In various embodiments, source/drain regions 370and 375 are composed of semiconductor material that islattice-mismatched to the semiconductor material of semiconductorchannel regions 340-342 as well as lattice-mismatched to the SIsemiconductor material of etched SI semiconductor layer 345. In anexemplary embodiment, semiconductor channel regions 340-342 are composedof a III-V semiconductor material, etched SI semiconductor layer 345 isa layer of epitaxial SI semiconductor material that is a lattice-matchedto the III-V semiconductor material, and source/drain regions 370 and375 are composed of a III-V semiconductor material that islattice-mismatched with both semiconductor channel regions 340-342 andthe SI semiconductor material of etched SI semiconductor layer 345. Inone example, SI semiconductor layer 345 is a layer of epitaxial Fe-dopedInP, semiconductor channel regions 340-342 are composed of ansemiconductor material that is lattice-matched to Fe-doped InP, such asIn_(0.53)Ga_(0.47)As, and source/drain regions 370 and 375 are composedof In_(y)Ga_((1−y))As where y>0.53 to enhance charge carrier transportin a p-FET device. Alternatively, another example would includesource/drain region compositions of In_(y)Ga_((1−y))As where y<0.53 toenhance charge carrier transport in an n-FET device. It should be notedthat the shape of the source/drain regions 370 and 375 augment thestrain experienced by semiconductor channel regions 340-342 as comparedto the shape of source/drain regions 360 and 365 and their effect onchannel regions 240-242 (FIG. 3A).

FIGS. 4-8 show processes for an exemplary embodiment of the presentinvention in which the gate structures are fabricated after thesource/drain regions.

FIG. 4A illustrates a cross-sectional view depicting the formation of aplurality of sacrificial gates 405-407 with adjoining spacers 410-413 onthe semiconductor layer 115 of FIG. 1B, in accordance with an exemplaryembodiment of the present invention. In various embodiments, sacrificialgates 405-407 are composed of any material or combination of materialsthat will act as a protecting layer during subsequent fabrication steps.In various embodiments, spacers 410-413 are composed of an insulatorsuch as SiO₂ or Si₃N₄. As shown in FIG. 4A, spacers 410-413 are adjacentto and in direct contact with the sacrificial gate elements andorthogonal to and in direct contact with semiconductor layer 115. Theformation of sacrificial gates as embodied by FIG. 4A is well understoodby those skilled in the art and, as such, a detailed description of suchprocesses is not presented herein.

FIG. 4B illustrates a cross-sectional view depicting the removal of thesemiconductor layer 115 along with a portion of the SI semiconductorlayer 110 adjacent to the spacers 410-413 from the structure depicted inFIG. 4A, thereby defining semiconductor channel regions 440-442 and anetched SI semiconductor layer 445 in accordance with an exemplaryembodiment of the present invention. In this embodiment, reactive ionetching (RIE) removes all of the semiconductor material and a portion ofthe SI semiconductor material between spacers 410 and 411 as well asbetween spacers 412 and 413 to create trenches 450 and 455. Although theembodiment described is created using RIE, other dry etching processeswill work to obtain the shown anisotropic etch. In this embodiment,semiconductor channel regions 440, 441, and 442 are created underneaththe sacrificial gate/spacer elements and rest on top of the highestsurfaces of etched SI semiconductor layer 445. The semiconductor channelregions 440-442 and the upper sidewalls of trenches 450 and 455 arecomposed of the semiconductor material of semiconductor layer 115. Theetched SI semiconductor layer 445 as well as the lower sidewalls andfloors of trenches 450 and 455 are composed of the SI semiconductormaterial of SI semiconductor layer 110.

FIG. 5A illustrates a cross-sectional view depicting the formation ofsource/drain regions 560 and 565 on the lower surfaces of the etched SIsemiconductor layer 445 and adjacent to the semiconductor channelregions 440-442 and spacers 410-413 of the structure depicted in FIG.4B, in accordance with an exemplary embodiment of the present invention.In various embodiments, source/drain regions 560 and 565 are composed ofsemiconductor material that is lattice-mismatched to the semiconductormaterial of semiconductor channel regions 440-442 as well aslattice-mismatched to the SI semiconductor material of etched SIsemiconductor layer 445. In an exemplary embodiment, semiconductorchannel regions 440-442 are composed of a III-V semiconductor material,etched SI semiconductor layer 445 is an etched layer of epitaxial SIsemiconductor material that is a lattice-matched to the III-Vsemiconductor material, and source/drain regions 560 and 565 arecomposed of another III-V semiconductor material that islattice-mismatched with both semiconductor channel regions 440-442 andthe SI semiconductor material of etched SI semiconductor layer 445. Forexample, SI semiconductor layer 445 includes a top layer of epitaxialFe-doped InP, semiconductor channel regions 440-442 are composed of analloy that is lattice-matched to Fe-doped InP, such asIn_(0.53)Ga_(0.47)As, and source/drain regions 560 and 565 are composedof In_(y)Ga_((1−y))As where y>0.53 to provide enhanced charge carriertransport in a p-FET device. Alternatively, another example wouldinclude source/drain region compositions of In_(y)Ga_((1−y))As wherey<0.53 to provide enhanced charge carrier transport in an n-FET device.Source/drain regions 560 and 565 are typically overgrown and thenpolished back by chemical mechanical polishing (CMP) so that they makean even top surface with sacrificial gates 405-407 and spacers 410-413.

FIG. 5B illustrates a cross-sectional view depicting the removal ofsacrificial gates 405-407 from the structure of FIG. 5A, formation ofgate dielectric layers 520-522 along the exposed spacer 410-413sidewalls and exposed semiconductor channel region 440-442 surfaces, andformation of gate conductors 505-507, in accordance with an exemplaryembodiment of the present invention. In various embodiments, gatedielectric layers 520-522 are composed of insulators such as silicondioxide or a high-k dielectric metal oxide such as hafnium oxide,hafnium silicon oxide, hafnium silicon oxynitride, lanthanum oxide,lanthanum aluminum oxide, zirconium oxide, zirconium silicon oxide,zirconium silicon oxynitride, tantalum oxide, titanium oxide, bariumstrontium titanium oxide, barium titanium oxide, strontium titaniumoxide, yttrium oxide, aluminum oxide, lead scandium tantalum oxide, andlead zinc niobate. In various embodiments, gate conductors 505-507 arecomposed of a conducting metal.

FIG. 6A illustrates a cross-sectional view depicting semiconductorchannel regions 640-642 on top of the upper surfaces of etched SIsemiconductor layer 645 with hard mask regions 605-607 on top ofsemiconductor channel regions 640-642, in accordance with an exemplaryembodiment of the present invention. In various embodiments,semiconductor channel regions 640-642 and etched SI semiconductor layer645 are composed of semiconductor and SI semiconductor materials,respectively, which are lattice-matched to each other. In someembodiments, semiconductor channel regions 640-642 are composed of aIII-V semiconductor material and etched SI semiconductor layer 645 iscomposed of an SI semiconductor material that is lattice-matched withsaid III-V semiconductor material. For example, semiconductor channelregions 640-642 are composed of In_(0.53)Ga_(0.47)As and etched SIsemiconductor layer is composed of Fe-doped InP. Hard mask regions605-607 are composed of any material that serves to protect underlyingstructural elements during fabrication processes. The formation of thestructures such as the one embodied by FIG. 4A is well understood bythose skilled in the art and, as such, a detailed description of suchprocesses is not presented herein.

FIG. 6B illustrates a cross-sectional view depicting the formation ofsource/drain regions 660-665 on the lower surfaces of the etched SIsemiconductor layer 645 and adjacent to the semiconductor channelregions 640-642 and hard mask regions 605-607 of the structure depictedin FIG. 6A, in accordance with an exemplary embodiment of the presentinvention. In various embodiments, source/drain regions 660 and 665 arecomposed of semiconductor material that is lattice-mismatched to thesemiconductor material of semiconductor channel regions 640-642 as wellas lattice-mismatched to the SI semiconductor material of etched SIsemiconductor layer 645. In an exemplary embodiment, semiconductorchannel regions 640-642 are composed of a III-V semiconductor material,etched SI semiconductor layer 645 is composed of an epitaxial SIsemiconductor material that is a lattice-matched to the III-Vsemiconductor material, and source/drain regions 660 and 665 arecomposed of a III-V semiconductor material that is lattice-mismatchedwith both the semiconductor channel regions 640-642 and the SIsemiconductor material of etched SI semiconductor layer 645. Forexample, SI semiconductor layer 645 is layer of epitaxial Fe-doped InP,semiconductor channel regions 640-642 are composed of an alloy that islattice-matched to Fe-doped InP, such as In_(0.53)Ga_(0.47)As, andsource/drain regions 660 and 665 are composed of In_(y)Ga_((1−y))Aswhere y>0.53 to enhance charge carrier transport in a p-FET device.Alternatively, another example would include source/drain regioncompositions where y<0.53 to enhance charge carrier transport in ann-FET device.

FIG. 7A illustrates a cross-sectional view depicting the removal of hardmask regions 605-607 from the structure depicted in FIG. 6B, inaccordance with an exemplary embodiment of the present invention. Afterthe removal of the hard mask, source/drain regions 660 and 665 projectupwards at a level higher than the newly exposed surfaces ofsemiconductor channel regions 640-642. The removal of hard mask regionssuch as regions 605-607 is well understood by those skilled in the artand, as such, a detailed description of such processes is not presentedherein.

FIG. 7B illustrates a cross-sectional view depicting the formation ofspacers 710-713 adjacent to the exposed sides of the source/drainregions 660 and 665 of the structure depicted in FIG. 7A, in accordancewith an exemplary embodiment of the present invention. The formation ofspacers such as spacers 710-713 is well understood by those skilled inthe art and, as such, a detailed description of such processes is notpresented herein.

FIG. 8A illustrates a cross-sectional view depicting the formation ofgate dielectric layers 820-822 over the exposed surfaces of thesemiconductor channel regions 640-642 and spacers 710-713 of thestructure depicted in FIG. 7B, in accordance with an exemplaryembodiment of the present invention. In various embodiments, gatedielectric layers 820-822 are composed of insulators such as silicondioxide or a high-k dielectric metal oxide such as hafnium oxide,hafnium silicon oxide, hafnium silicon oxynitride, lanthanum oxide,lanthanum aluminum oxide, zirconium oxide, zirconium silicon oxide,zirconium silicon oxynitride, tantalum oxide, titanium oxide, bariumstrontium titanium oxide, barium titanium oxide, strontium titaniumoxide, yttrium oxide, aluminum oxide, lead scandium tantalum oxide, andlead zinc niobate. The formation of gate dielectric layers such aslayers 820-822 is well understood by those skilled in the art and, assuch, a detailed description of such processes is not presented herein.

FIG. 8B illustrates a cross-sectional view depicting the formation ofgate conductors 830-832 on the gate dielectric layers 820-822 of thestructure depicted in FIG. 8A, in accordance with an exemplaryembodiment of the present invention. In various embodiments gateconductors 830-832 are composed of a conducting material, such as ametal. The formation of gate conductors such as conductors 830-832 iswell understood by those skilled in the art and, as such, a detaileddescription of such processes is not presented herein.

FIG. 8C illustrates a cross-sectional view depicting recessedsource/drain regions 860 and 865 in a structure analogous to the onedepicted in FIG. 8B, in accordance with an exemplary embodiment of thepresent invention. The elements seen in the embodiment exemplified byFIG. 3B are analogous to those in FIG. 8B. Gate conductors 850-852 aredeposited on gate dielectric layers 870-872. Spacers 810 and 811 abutthe sidewall portions of source/drain region 865 that project abovesemiconductor channel region 842 and 841, respectively. Spacers 812 and813 abut the sidewall portions of source/drain region 860 that projectabove semiconductor channel region 841 and 840, respectively.Source/drain regions 860 and 865 rest on the lower surfaces of etched SIsemiconductor layer 845. Source/drain region 860 is between and indirect contact with semiconductor channel regions 840 and 841.Source/drain region 865 is between and in direct contact withsemiconductor channel regions 84 and 842.

Like the structure illustrated in FIG. 3B, the wedging of source/drainregions 860 and 865 underneath semiconductor channel regions 840-842augments the strain on semiconductor channel regions 840-842 compared tothe un-wedged source/drain structures 660 and 665 illustrated in FIG.8B. In various embodiments, source/drain regions 860 and 865 arecomposed of semiconductor material that is lattice-mismatched to thesemiconductor material of semiconductor channel regions 840-842 as wellas lattice-mismatched to the SI semiconductor material of etched SIsemiconductor layer 845. In an exemplary embodiment, semiconductorchannel regions 840-842 are composed of a III-V semiconductor material,etched SI semiconductor layer 845 is composed of epitaxial SIsemiconductor material that is a lattice-matched to the III-Vsemiconductor material, and source/drain regions 860 and 865 arecomposed of a III-V semiconductor material that is lattice-mismatchedwith both semiconductor channel regions 840-842 and the top layermaterial of etched SI semiconductor layer 845. For example, SIsemiconductor layer 845 is composed of epitaxial Fe-doped InP,semiconductor channel regions 840-842 are composed of an alloy that islattice-matched to Fe-doped InP, such as In_(0.53)Ga_(0.47)As, andsource/drain regions 860 and 865 are composed of In_(y)Ga_((1−y))Aswhere y>0.53 to provide enhanced charge carrier transport in a p-FETdevice. Alternatively, another example would include source/drain regioncompositions where y<0.53 to provide enhanced charge carrier transportin an n-FET device.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiment, the practical application or technicalimprovement over technologies found in the marketplace, or to enableother of ordinary skill in the art to understand the embodimentsdisclosed herein.

The methods and structures as described above are used in thefabrication of integrated circuit chips. The resulting integratedcircuit chips can be distributed by the fabricator in raw wafer form(that is, as a single wafer that has multiple unpackaged chips), as abare die, or in a packaged form. In the latter case the chip is mountedin a single chip package (such as a plastic carrier, with leads that areaffixed to a motherboard or other higher level carrier) or in amultichip package (such as a ceramic carrier that has either or bothsurface interconnections or buried interconnections). In any case thechip is then integrated with other chips, discrete circuit elements,and/or other signal processing devices as part of either (a) anintermediate product, such as a motherboard, or (b) an end product. Theend product can be any product that includes integrated circuit chips,ranging from toys and other low-end applications to advanced computerproducts having a display, a keyboard or other input device, and acentral processor.

What is claimed is:
 1. A method of forming a semiconductor structurecomprising: forming a layer of a first semiconductor material on top ofa layer of a semi-insulating semiconductor material, wherein the firstsemiconductor material and the semi-insulating semiconductor materialare lattice-matched; etching the layer of first semiconductor materialto a depth that, at least, exposes the semi-insulating semiconductormaterial and forms a semiconductor channel region, wherein thesemiconductor channel region has a first end and a second end; andforming a first source/drain region at the first end of thesemiconductor channel region and a second source/drain region at thesecond end of the semiconductor channel region, wherein the firstsource/drain region and the second source/drain region are furthercomprised of a second semiconductor material, wherein the secondsemiconductor material is lattice-mismatched to the first semiconductormaterial and to the semi-insulating semiconductor material.
 2. Themethod of claim 1, wherein the etching step provides an isotropic etch.3. The method of claim 1 further comprising: fabricating a gatestructure on top of the layer of the first semiconductor material. 4.The method of claim 1 further comprising: fabricating a gate structureon top of the semiconductor channel region such that the gate structureis between the first source/drain region and the second source/drainregion.
 5. The method of claim 1, wherein one or both of the firstsemiconductor material and the second semiconductor material are furthercomprised of compound semiconductors.
 6. The method of claim 1, whereinone or both of the first semiconductor material and the secondsemiconductor material are further comprised of III-V semiconductors. 7.The method of claim 1, wherein one or both of the first semiconductormaterial and the second semiconductor material include indium.
 8. Themethod of claim 1, wherein one or both of the first semiconductormaterial and the second semiconductor material are further comprised ofalloys of indium arsenide and gallium arsenide.